1. Field of the Invention
The invention relates to a method and a device for optically focusing a projection image projected by a projector, and in particular for use in fixed image projectors or film projectors.
2. Description of the Related Art
Various technical methods for optical focusing are known from the prior art, where focusing occurs without intervention by an operator. Such methods are therefore often referred to by the term “autofocus”.
Common autofocusing methods fundamentally provide methods that are based on a phase comparison and/or a contrast measurement of at least one object. In the latter methods, using contrast measurement, an image distance of an object varies, for example, until a measured contrast has achieved a maximum level. However, such contrast methods are only necessarily suitable for objects with a low contrast, i.e., objects or projections with a high proportion of monochrome and low-contrast background information, or with very little colour or grey contrast.